This relates to image sensors and, more particularly, to image sensors with passivation layers that have radially-varying refractive index profiles.
Digital cameras are often provided with digital image sensors such as CMOS (complementary metal-oxide-semiconductor) image sensors. Digital cameras may be stand-alone devices or may be included in electronic devices such as cellular telephones or computers. A typical CMOS image sensor has an array of image sensor pixels containing contain thousands or millions of pixels. Lenses focus incoming light onto the array of pixels. Each pixel typically has a microlens for focusing light onto a photosensitive element such as a photodiode. Layers such as a dielectric stack, a passivation layer, and a color filter layer may be located between the microlens and photodiode. Metal interconnects and vias can be formed in the metal and dielectric layers of the dielectric stack. The passivation layer can be formed above the dielectric stack. A color filter layer can contain filters for filtering light of different colors.
Image sensor performance is influenced by the efficiency with which image sensor pixels gather light. An image sensor could have better performance if light were focused more precisely onto each pixel's photosensitive element. Improved pixel structures may therefore be desired for focusing light within an image sensor pixel.